JP3312483B2 - Reverse osmosis treatment method and desalination method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to desalination by reverse osmosis,
The present invention relates to a separation method, and particularly to a method for producing ultrapure water, desalination of seawater, desalination of seawater, reuse of wastewater, and the like.

[0002]

2. Description of the Related Art Separation techniques using membranes are used in a wide range of fields such as desalination of seawater and canned water, medical treatment, production of industrial pure water and ultrapure water, and industrial wastewater treatment. In the separation by these membranes, contamination of the separation device by microorganisms increases fine particles and TOC (total organic carbon) in the liquid to be treated, deteriorating the quality of permeated water obtained, and causing microorganisms on the membrane surface. Propagation of the membrane, or propagation of organic substances consisting of microorganisms and their metabolites, etc.
Problems such as a decrease in separability occur. Therefore, sterilization of the membrane separation device is an important technique for performing membrane separation.
Various methods of sterilizing a membrane separation device have been proposed, and generally a method of constantly or intermittently adding a sterilizing agent to a feed solution has been adopted.

As a disinfectant, a chlorine-based disinfectant has been used for a long time. Recently, however, a new type of disinfectant such as chloramines, hydrogen peroxide, peracetic acid, sodium bisulfite, etc. is used in accordance with the membrane used. Sterilization methods have been proposed. However, at present, chlorine-based disinfectants are used because of their cost and ease of operation. Reverse osmosis membranes are chemically degraded by oxidizing substances such as chlorine due to the characteristics of the material. Recently, a film material having relatively high oxidation resistance has been developed, but its durability cannot be said to be sufficient. Therefore, generally, the supply liquid is sterilized using a bactericide such as a chlorine-based bacterium, and the separation operation is performed by reducing free chlorine using a reducing agent before supplying to the reverse osmosis membrane. Sodium sulfite and sodium hydrogen sulfite are widely used as reducing agents.

On the other hand, a chelating agent is used in a reverse osmosis membrane device such as a water treatment facility or a desalination device of an evaporation method, but its purpose is mainly to use scale materials such as silica and heavy metals in a device. This is to suppress precipitation, and has been used particularly in treating water having a large amount of silica scale components. For example, Japanese Patent Application Laid-Open No. Sho 53-30482 discloses that the life of a reverse osmosis membrane can be extended by performing reverse osmosis treatment after reducing the calcium and magnesium by bringing a supply liquid into contact with a chelating resin in advance. 52-1516
No. 70 and JP-A-4-4022 disclose a method of adding a phosphate to prevent the generation of scale in a reverse osmosis device. Also, JP-A-63-218773, JP-A-4-99199, and JP-B-5-1403.
No. 9 discloses a method of recovering paint and copper by adding a chelating agent to waste water of electrodeposition paint and copper plating and performing reverse osmosis concentration. Further, JP-A-63-6958
No. 6 and JP-A-2-293027 disclose a method of supplying a solution to which chlorine or an oxidizing agent and a phosphate are added to perform sterilization and stable operation of a reverse osmosis membrane device.

[0005]

Normally, by using a disinfectant and sodium sulfite or sodium bisulfite, desalinated water can be stably produced in a reverse osmosis membrane device without being affected by generation of microorganisms and deterioration of membrane performance due to the disinfectant. Can be manufactured. However, in recent years, it has been found that there is a phenomenon in which the membrane performance is reduced despite the operation in the absence of free chlorine by adding sodium bisulfite, and the conventional operation method is not always sufficient. Has become apparent. It has become clear that this phenomenon has also occurred in polyamide-based reverse osmosis membranes and cellulose acetate-based membranes which are said to have higher resistance to oxidants.

[0006] When the reverse osmosis membrane separation device is stopped, it is generally stopped as it is, or after replacing the feed solution with demineralized water, or by adding bisulfite to the solution on the feed solution side. Have been. Normally, there is no problem with these stopping methods, but it has been found that despite the recent use of these stopping methods, the film performance may be reduced by stopping, which is not necessarily sufficient. Have been.

[0007]

To achieve the above object, the present invention has the following arrangement.

[0008] That is, " when supplying a supply liquid to a separation apparatus having a reverse osmosis membrane, a reducing agent is added to the supply liquid, and then the separation apparatus is stopped, and during this stop state,
A reverse osmosis treatment method comprising adding a chelating agent to a supply liquid. It is about.

The present inventors have investigated the cause of the problem that the performance of the membrane deteriorates despite the fact that oxidizing substances such as chlorine have been completely eliminated with a reducing agent during the operation of the reverse osmosis membrane apparatus, and examined the countermeasures. As a result, in systems where ions such as copper and chromium are present in extremely small amounts, these heavy metals act as catalysts, and the reducing agent reacts to form oxidizing substances. It has been found that a decrease in membrane performance can be suppressed by adding a much lower concentration than that usually used as a chelating agent.

[0010] That is, the present inventors have found that when producing desalinated water using a reverse osmosis membrane device, a decrease in membrane performance, which is a problem,
Despite reducing the fungicide with a reducing agent,
We are diligently examining the problem of reduced membrane performance, and by reducing the germicide with a reducing agent and adding a chelating agent to the feed water, it is possible to significantly suppress the performance degradation of the membrane and stably produce desalinated water. The heading has reached the present invention.

In the present invention, a reverse osmosis membrane separation apparatus is an apparatus for supplying a liquid to be treated to a reverse osmosis membrane module under pressure for the purpose of water production, concentration, separation, etc., and separating the liquid into a permeate and a concentrate. Usually refers to reverse osmosis membrane element, pressure vessel,
It is composed of a pressure pump and the like. The liquid to be separated supplied to the reverse osmosis membrane device is usually a bactericide, a flocculant, a reducing agent,
Addition of a chemical such as a pH adjuster and pretreatment such as sand filtration, activated carbon filtration, and security filter are performed. For example, in the case of seawater desalination, after taking in seawater, particles and the like are separated in a sedimentation basin, and a bactericide is added here to perform sterilization.
Further, sand filtration is performed by adding a flocculant such as iron chloride. The filtrate is stored in a storage tank, and after adjusting the pH with sulfuric acid or the like, is sent to a high-pressure pump. A reducing agent such as sodium hydrogen sulfite is added to the liquid to remove the germicide, and after passing through a security filter, the pressure is increased by a high-pressure pump and supplied to the reverse osmosis module. However, these pre-processing
It is appropriately adopted according to the type of the supply liquid to be used and the application.

Here, the reverse osmosis membrane is a semipermeable membrane that allows some components in the liquid mixture to be separated, for example, a solvent to pass through but not other components. As the material, polymer materials such as cellulose acetate polymer, polyamide, polyester, polyimide, and vinyl polymer are often used. The membrane structure has a dense layer on at least one surface of the film, and an asymmetric film having fine pores having a large pore diameter gradually from the dense layer toward the inside of the film or the other surface. There are composite membranes with a very thin active layer formed of a material. The membrane form includes a hollow fiber and a flat membrane. However, the method of the present invention can be used irrespective of the material, membrane structure and membrane form of the reverse osmosis membrane, and is very effective. Typical reverse osmosis membranes include, for example, a cellulose acetate-based or polyamide-based asymmetric membrane and a composite membrane having a polyamide-based or polyurea-based active layer. Among them, the method of the present invention is effective for cellulose acetate-based asymmetric membranes and polyamide-based composite membranes, and is particularly effective for aromatic polyamide-based composite membranes.

Examples of the cellulose acetate-based membrane include cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, and the like, or a mixture of these organic acid esters or a mixture thereof. Can be As the polyamide film, aliphatic, aromatic polyamide and linear polymer,
Crosslinked polymers are included.

A reverse osmosis membrane module is formed by actually using the above reverse osmosis membrane. The flat membrane is incorporated in a spiral, tubular, plate and frame module, and the hollow fiber is Although it can be used after being bundled and assembled in a module, the present invention is not limited to the form of these reverse osmosis membrane modules.

Generally, a bactericide added at the pretreatment stage of a reverse osmosis membrane device is added to prevent the growth and adhesion of fungi and microorganisms in a feed solution or a pretreatment device. Chlorine disinfectants, hydrogen peroxides, peracetic acids, chloramines and the like can be used. Generally, an oxidizing substance is easily used in terms of germicidal power, and a chlorine-based germicide is easy to use because of its price, bactericidal power, and easy handling.

The concentration of the bactericide depends on the quality of the feed water to be used, but is generally 0.1 to 5 after addition to the feed solution.
In the case of a chlorine-based disinfectant, the residual chlorine concentration in the feed solution is 0.1 to 50 ppm. Considering that the amount of the reductant to be added is reduced and that the minimum necessary amount for disinfection is considered. 1 to 20 ppm, more preferably 0.1
-10 ppm. Residual chlorine refers to the sum of free chlorine and bound chlorine, and the residual chlorine concentration is measured according to JIS-K01.
The method can be easily performed by the ortho-tolidine method described in No. 01, for example.

When a reverse osmosis membrane comes into direct contact with an oxidizing germicide, particularly a chlorine-based germicide, the membrane performance is reduced. In particular, a polyamide-based or polyurea-based composite membrane is inferior in chlorine resistance as compared with a cellulose acetate-based asymmetric membrane, and a cellulose acetate-based asymmetric membrane significantly deteriorates depending on conditions such as pH. Therefore, in many actual plants, when a chlorine-based disinfectant is used, a reducing agent is added and left before the liquid to be treated is supplied to the reverse osmosis membrane module in order to prevent the chlorine from directly contacting the reverse osmosis membrane. It is necessary to reduce the fungicide. It is preferable to add a reducing agent to stabilize the operation even when using a bactericide such as chloramines which has no or little effect on membrane performance, and to cope with troubles.

As the reducing agent, those which are water-soluble, have a large reducing property and do not affect the reverse osmosis membrane can be used. Further, sodium sulfite, sodium hydrogen sulfite, and the like are preferable because they are inexpensive and easy to handle. The concentration of the reducing agent used must be sufficient to eliminate any germicide remaining in the feed. In addition, since the reducing agent also reacts with oxygen dissolved in the supply liquid, it is preferable to add the disinfectant in an amount of 1 to 10 times the amount of the disinfectant in consideration of the amounts of the remaining disinfectant and dissolved oxygen. Further, in consideration of completely eliminating the germicide and reducing the amount of the reducing agent used, a reducing agent having an equivalent amount of 1.1 to 5 times the germicide is preferable. Usually, since the reducing agent is added in excess of the germicide, the unreacted reducing agent or its reaction product is mixed in the feed liquid of the reverse osmosis membrane device.

In the present invention, the chelating agent to be added to the feed solution of the reverse osmosis membrane device forms a complex with a metal or metal ion in the solution to solubilize or coagulate and precipitate the metal. Inorganic ionic polymers or monomers can be used. As the ionic polymer, synthetic polymers such as polyacrylic acid, sulfonated polystyrene, polyacrylamide, and polyallylamine, and natural polymers such as carboxymethylcellulose, chitosan, and alginic acid can be used. Ethylenediaminetetraacetic acid or the like can be used as the organic monomer. As the inorganic chelating agent, polyphosphate, polyaluminum chloride and the like can be used. Among these chelating agents, polyphosphate and ethylenediaminetetraacetic acid (EDTA) are particularly preferably used in the present invention in terms of availability, ease of operation such as solubility, and price. The polyphosphate refers to a polymerized inorganic phosphoric acid-based substance having two or more phosphorus atoms in a molecule represented by sodium hexametaphosphate and bonded to an alkali metal or an alkaline earth metal by a phosphoric acid atom or the like. Representative polyphosphates include tetrasodium pyrophosphate, disodium pyrophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, sodium heptapolyphosphate, sodium decapolyphosphate, sodium metaphosphate, sodium hexametaphosphate, and potassium salts thereof. can give.

It is sufficient that the concentration of the chelating agent is at least an amount capable of taking in the heavy metal in the feed solution. However, in consideration of operability such as cost and time required for dissolution, it is generally 0.01%. １００100 ppm, which depends on the quality of the feedwater, but usually 50 to 10,000 times the concentration of heavy metals contained in the feedwater, and 0.1 to 0.1 times in the case of seawater.
1 to 20 ppm is preferable, and more preferably 0.1 to 20 ppm.
10 ppm. When the addition amount is less than 0.01 ppm, the action of the heavy metal cannot be sufficiently suppressed, so that the film performance deteriorates. Further, at 100 ppm or more, the chelating agent itself is adsorbed on the membrane surface to reduce the amount of fresh water,
It is not preferable because it deteriorates water quality. In a feed solution containing a large amount of scale substance or heavy metal, addition of several tens to several hundreds ppm may be necessary. On the other hand, the chelating agent of the present invention is characterized in that the effect can be sufficiently obtained at a concentration lower than that generally used as a scale inhibitor, and the chemical cost required for operating the apparatus is reduced. For example, polyphosphate is a chemical used as a scale inhibitor such as calcium carbonate in seawater or hard water in the operation of a reverse osmosis membrane device, and as a rust inhibitor for metals of piping materials. In such a case, usually 100 ppm is used. The above addition is necessary.

We have found that in feed systems where sodium bisulfite is present, heavy metals, especially copper, are present in the feed.
When metals such as cobalt, chromium, and nickel are present, these heavy metals act as catalysts to convert sulfite ions into sulfite radicals, which form oxidizing persulfuric acid, which further reacts with chlorine ions in the feed solution. It has been found that perchlorate ions and chlorine are generated by the reaction.

In the present invention, it is considered that the chelating agent acts on the heavy metal present in the supply liquid, forms a chelate compound with the heavy metal, and blocks the catalytic action of the heavy metal. Therefore, it is considered that a sufficient amount of the chelating agent acting on the heavy metal present in a small amount can sufficiently exert the effect.

The chelating agent is certainly used in a reverse osmosis membrane device such as a water treatment facility or a desalination device of an evaporation method, but the purpose is different from the present invention, and mainly the silica, the heavy metal and the like are used. Is to suppress the deposition of the scale material in the apparatus. Therefore, the effect of adding a chelating agent in an atmosphere where a reducing agent is present as in the present invention has not been disclosed at all. In addition, in the conventional addition method, the concentration of the scale agent was at the level of several tens of ppm.
It was not known at all that the addition of a small amount had the effect of suppressing the performance change of the reverse osmosis membrane.

Examples of the supply liquid for the reverse osmosis membrane device include a solution containing a reducing agent obtained by pretreating can water such as river water and groundwater, seawater, and industrial wastewater. The present invention can obtain the effect with any of the supply liquids, but is particularly effective in the case of seawater.

The stoppage of the reverse osmosis membrane separation apparatus in the present invention means that the operation of the reverse osmosis membrane apparatus is stopped for a predetermined time due to pretreatment of the plant, trouble or periodic inspection of the reverse osmosis membrane separation apparatus, or other reasons. It refers to the case. The outage time can be minutes to days, long months to years. The method of adding a chelating agent at the time of stoppage of the present invention is particularly effective for maintaining the membrane performance against the phenomenon that the membrane performance decreases during the stoppage. The production of an oxidizing substance from bisulfite or the like by heavy metal ions requires a reaction time of several seconds to several minutes, but during normal operation, the supply liquid is always flowing, so the oxidant is generated before the oxidant is generated. Is discharged and, depending on the plant, a decrease in membrane performance may not be observed. However, at the time of stoppage, the liquid does not flow, and an oxidizing substance is generated in the liquid in contact with the membrane, causing deterioration of the membrane performance. Therefore, the present invention is particularly effective when the vehicle stops.

[0026]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

In the examples, the exclusion (desalting) rate was determined by the following equation.

Rejection rate (%) = {1- (concentration of solute in permeate) / (concentration of solute in feed)} × 100 The salt permeation rate (SP) is shown by subtracting the rejection rate from 100.

The amount of fresh water was determined by the amount of permeated water permeating the membrane per unit time per unit time or the amount of permeated water permeating the element per unit time.

REFERENCE EXAMPLE 1 A UTC-70 membrane manufactured by Toray, which is an aromatic polyamide composite membrane, was set in a reverse osmosis membrane evaluation apparatus, and the pressure was 15 kg / cm ² and the pH was 6.5 using a 1500 ppm saline solution as a supply liquid. When reverse osmosis separation was performed, the desalination rate was 99.71% (S
P = 0.29), and the amount of fresh water was 1.1 m ³ / m ² · d.
Further, when the apparatus was continuously operated under the same conditions, the desalination rate was 99.68% (SP = 0.3) after 100 hours.
2) Dewatering amount 1.1 m ³ / m ² · d, after 500 hours, desalting rate 99.67% (SP = 0.33), fresh water amount 1.09 m
³ / m ² · d and after 1000 hours the desalination rate is 99.6
7% (SP = 0.33), fresh water production 1.08 m ³ / m ² · d
Met.

REFERENCE EXAMPLE 2 A UTC-80 membrane manufactured by Toray, which is an aromatic polyamide composite membrane, was set in a reverse osmosis membrane evaluation apparatus, and the pressure was 56 kg / cm ² and the pH was 6.7 using 35,000 ppm saline as a supply liquid. When reverse osmosis separation was performed, the desalination rate was 99.51%.
(SP = 0.49), and the amount of fresh water was 0.7 m ³ / m ² · d. Further, when the apparatus was continuously operated under the same conditions, after 100 hours, the desalting rate was 99.51% (SP = 0.
49), water production 0.68 m ³ / m ² · d, after 500 hours,
Desalination rate 99.50% (SP = 0.50), water production 0.6
7 m ³ / m ² · d and after 1000 hours the desalination rate is 9
9.48% (SP = 0.52), water production 0.66 m ³ / m
It was ² · d.

Example 1 A Toray UTC-70 membrane, which is an aromatic polyamide composite membrane, was set in a reverse osmosis membrane evaluation apparatus, and 1500 ppm of a saline solution was used as a feed solution, and 50 ppb of copper and 20 ppm of sodium bisulfite were added thereto. When 5 ppm of sodium hexametaphosphate was added thereto and subjected to reverse osmosis separation under the conditions of a pressure of 15 kg / cm ² and a pH of 6.6, a desalination rate of 99.72% was obtained.
The amount of fresh water was 1.1 m ³ / m ² · d. Further, when the apparatus was continuously operated under the same conditions, after 100 hours,
Desalination rate 99.69% (SP = 0.31), fresh water production 1.0
9 m ³ / m ² · d, after 500 hours, desalination rate 99.67%
(SP = 0.33), the amount of fresh water is 1.07 m ³ / m ² · d, and after 1000 hours, the desalination rate is 99.66% (SP =
0.34), and the amount of fresh water was 1.07 m ³ / m ² · d.

Example 2 A Toray UTC-80 membrane, which is an aromatic polyamide composite membrane, was set in a reverse osmosis membrane evaluation apparatus, and 35,000 ppm of a saline solution was used as a feed solution. 10 ppb of copper and 20 ppm of sodium bisulfite were added thereto. Reverse osmosis separation was performed under conditions of a pressure of 56 kg / cm ² and a pH of 6.6 by adding 10 ppm of sodium hexametaphosphate, and the desalting rate was 99.50.
% (SP = 0.50) and the amount of fresh water was 0.67 m ³ / m ² · d. Further, when the apparatus was continuously operated under the same conditions, after 100 hours, the desalination rate was 99.51% (SP =
0.49), desalination rate 0.66 m ³ / m ² · d, after 500 hours, desalination rate 99.49% (SP = 0.51), desalination rate 0.65 m ³ / m ² · d Yes, after 1000 hours, desalination rate is 99.47% (SP = 0.53), fresh water production 0.65m
³ / m ² · d.

Example 3 Reverse osmosis separation was carried out in the same manner as in Example 2 except that 10 ppm of sodium hexametaphosphate was changed to 5 ppm of ethylenediaminetetraacetic acid (EDTA).
9.51% (SP = 0.49), water production 0.69 m ³ / m
It was ² · d. Further, when the apparatus was continuously operated under the same conditions, the desalination rate was 99.49% after 100 hours.
(SP = 0.51), fresh water production 0.68 m ³ / m ² · d, 5
After 00 hours, the desalting rate is 99.48% (SP = 0.52),
The amount of fresh water is 0.69 m ³ / m ² · d, and after 1000 hours,
The desalination rate is 99.46% (SP = 0.54), and the amount of fresh water is 0.4.
It was 65 m ³ / m ² · d.

Example 4 Copper 10 ppb, chromium 10 ppb, nickel 10 ppb
20 ppm of sodium bisulfite was added to a solution obtained by performing a pretreatment such as chlorine sterilization and sand filtration on seawater containing, and the pH was adjusted to 6.7 with sulfuric acid. Then, 10 ppm of sodium hexametaphosphate was added thereto, and 25 ° C. in the feed solution was raised to 56 kg / cm ² was supplied to Toray Industries, reverse osmosis membrane module SU-810, was carried out the operation at a recovery rate of 10%. Initial desalination rate 9
9.66% (SP = 0.34), water production 4.3 m ³ / m ²
・ D. Further, when the apparatus was continuously operated under the same conditions, the desalination rate was 99.66% after 100 hours.
(SP = 0.34), fresh water production 4.2 m ³ / m ² · d, 50
After 0 hour, the desalination rate is 99.65% (SP = 0.35) and the water production is 4.0 m ³ / m ² · d. After 1000 hours, the desalination rate is 99.65% (SP = 0). .35), water production 4.1 m
³ / m ² · d.

[0036]

Comparative Example 1 Reverse osmosis separation was carried out in the same manner as in Example 1 except that sodium hexametaphosphate was not added. Desalination was 99.68% (SP = 0.32), and the amount of water produced was 1. 1 m ³ / m
It was ² · d. Further, when the apparatus was continuously operated under the same conditions, the desalting rate was 99.55% after 100 hours.
(SP = 0.45), fresh water production 1.15 m ³ / m ² · d, 5
After 00 hours, the desalination rate was 99.32% (SP = 0.68),
The amount of fresh water is 1.17 m ³ / m ² · d, and after 1000 hours,
The desalination rate is 98.85% (SP = 1.15), and the amount of fresh water is 1.
It was 3 m ³ / m ² · d.

Comparative Example 2 Reverse osmosis separation was carried out in the same manner as in Example 2 except that sodium hexametaphosphate was not added. As a result, the desalination ratio was 99.48% (SP = 0.52), and the amount of water produced was 0. 68 m ³
/ m ² · d. Furthermore, when the apparatus was continuously operated under the same conditions, the desalination ratio was 99.22 after 100 hours.
% (SP = 0.78), fresh water production 0.69 m ³ / m ² · d,
After 500 hours, the desalination rate was 98.83% (SP = 1.1
7) The desalination amount is 0.75 m ³ / m ² · d. After 1000 hours, the desalination rate is 98.40% (SP = 1.60), and the desalination amount is 0.81 m ³ / m ² · d. Met.

Comparative Example 3 Reverse osmosis separation was carried out in the same manner as in Example 4 except that sodium hexametaphosphate was not added. The initial desalination ratio was 99.65% (SP = 0.35), and the water production amount was 4 .2 m
³ / m ² . Further, when the apparatus was continuously operated under the same conditions, the desalination rate was 99.48% after 100 hours.
(SP = 0.52), desalination amount 4.4 m ³ / m ² , after 500 hours, desalination rate 99.21% (SP = 0.79), desalination amount 4.4 m ³ / m ² After 1000 hours, the desalination rate is 9
8.51% (SP = 1.49), water production 4.4 m ³ / m ²
Met.

Example 5 Copper 10 ppb, chromium 10 ppb, nickel 10 ppb
20 ppm of sodium hydrogen sulfite was added to a solution obtained by performing a pretreatment such as chlorine sterilization and sand filtration on seawater containing water, the pH was adjusted to 6.7 with sulfuric acid, and the pressure was increased to 56 kg / cm ² at 25 ° C. Supply liquid to Toray reverse osmosis membrane module SU-81
0 and operated at a recovery of 10%. Initial desalination rate 99.63% (SP = 0.37), fresh water production 4.4 m ³
/ m ² . After the operation for 24 hours, the supply side was replaced with a 1000 ppm aqueous solution of sodium bisulfite containing 10 ppm of sodium hexametaphosphate, and then the apparatus was stopped. After stopping for 10 days, the operation was performed again under the above-mentioned conditions, and the desalination rate was 99.61% (SP = 0.39).
The amount of fresh water was 4.3 m3 / d.

Comparative Example 4 The reverse osmosis separator was operated, stopped and restarted in the same manner as in Example 5 except that sodium hexametaphosphate was not added to the replacement liquid at the time of stoppage. 9
9.64% (SP = 0.36), water production 4.3 m ³ /
m ² , desalination after stopping 99.22% (SP = 0.78),
The amount of fresh water was 4.5 m ³ / m ² .

[0042]

According to the present invention, a conventional method for producing desalinated water with a reverse osmosis membrane apparatus has been proposed in which a sterilizing agent is added and a sterilizing agent is eliminated with a reducing agent in order to stably operate the apparatus. Nevertheless, by adding a small amount of a chelating agent to the feed liquid, the reverse osmosis membrane performance was reduced and the membrane performance was reduced when the reverse osmosis membrane device was stopped. Therefore, desalinated water can be produced stably, reliably, and economically.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-21604 (JP, A) JP-A-2-293027 (JP, A) JP-A-63-69586 (JP, A) (58) Field (Int. Cl. ⁷ , DB name) B01D 61/00-69/14

Claims (11)

(57) [Claims] When a supply liquid is supplied to a separation apparatus having a reverse osmosis membrane, a reducing agent is added to the supply liquid, and then the separation apparatus is stopped. During this stop state, a chelating agent is added to the supply liquid. Reverse osmosis treatment method characterized by adding. 2. The reverse osmosis treatment method according to claim 1, wherein sodium sulfite or sodium hydrogen sulfite is used as the reducing agent. 3. A copper ions, cobalt ions, using a chelating agent capable of forming at least one ion complexes selected from the group consisting of chromium ions and nickel ions, reverse osmosis according to claim 1 or 2 Processing method. As wherein the chelating agent, used polyphosphate or ethylene diamine tetraacetic acid, reverse osmosis treatment method according to any one of claims 1-3. 5. The reverse osmosis treatment method according to claim 4 , wherein hexametaphosphate is used as the polyphosphate. 6. using the cellulose-based or membrane of polyamide as a reverse osmosis membrane, reverse osmosis treatment method according to any one of claims 1-5. 7. The reverse osmosis treatment method according to claim 6 , wherein a cellulose acetate membrane is used as the cellulose membrane, or an aromatic polyamide membrane is used as the polyamide membrane. 8. The reverse osmosis membrane is a composite membrane according to claim 1-7
The reverse osmosis treatment method according to any one of the above. 9. A chelating agent having a concentration of 0.01 to 1;
The addition is performed so as to be within the range of 00 ppm.
8. The reverse osmosis treatment method according to any one of 8 above. 10. A chelating agent having a concentration of 0.1-2.
The reverse osmosis treatment method according to claim 9 , wherein the addition is performed so as to be within a range of 0 ppm. 11. A fresh water producing method using the reverse osmosis treatment method according to any one of claims 1 to 10 .